Water is commonly employed in coal crushing and washing operations as a vehicle and to collect and suppress fines. However, water is desirably removed from cleaned coal prior to delivery of the product to a user for two important reasons. First, surface moisture much in excess of about five per cent can result in serious freezing of coal in railroad cars when shipment is made in sub-freezing weather. Second, and more importantly, any included moisture acts as a B.T.U. thief, the fuel value of clean coal being an inverse function of its moisture content.
In the past, partial dewatering of coal slurries has been accomplished by such procedures as filtration and centrifugation, sometimes followed by thermal drying to a target moisture level. In addition, dewatering aids have been utilized heretofore in instances where the cost effectiveness of the chemical additives exceeded the incremental equipment charges and related energy costs. One commonly employed dewatering aid has been a surface active chemical species known generically as sodium dialkylsulfosuccinate; but this material is often prohibitively expensive in its application; and usually exhibits a very significant foaming tendency, and therefore has limited utility.
Generally similar considerations obtain with respect to other particulate mineral masses.